This invention relates to method and apparatus for making stream feeders or bushings for flowing streams of heat-softened mineral material, such as glass, and more especially to a method and apparatus for producing a stream flow section or tip section of a feeder or bushing.
In the art of processing heat-softenable mineral material, such as glass into fibers or filaments and particularly continuous filaments used in the manufacture of textiles, it is standard practice to employ a receptacle, feeder or bushing having a bottom wall or floor provided with a plurality of orifices. Streams of heat-softened material flow through the orifices and are attenuated into fibers or filaments. It has been a practice to fashion the bottom wall or floor of the feeder of a platinum and rhodium alloy with projections through which the orifices are formed. The small orificed projections or tips help to prevent flooding of the molten glass across the bottom wall of the feeder. Also the projections aid the cooling of the minute glass streams emitted therefrom for attenuation into fibers.
Development in the art of forming textile fibers or filaments or glass is toward the production of textile strands of extremely fine filaments wherein thousands of filaments comprising one strand are drawn from streams of heat-softened glass from a single feeder. It therefore becomes imperative to fashion the orificed projections in close relation with proper spacing of the tips or projections. Also it is important that the projections be of uniform size and bore or passageway size to promote a uniform glass stream size so that fine filaments or fibers attenuated from the streams are of uniform character.
Endeavors have been made to fabricate or manufacture a feeder or bushing tip section by drilling holes in a plate, inserting flanged eyelet-like members in the openings and electric resistance welding the flanges on the eyelets to the floor or bottom plate to form a tip section. The preformed eyelets provide a convenient way to make the necessary projections or tips. A method of this character is disclosed in the Leedy and Russell U.S. Pat. No. 2,933,590. In this method the entire flange of an eyelet member is fused during electric resistance welding. However, because the electrode is in direct contact with the fused metal of the eyelet member, there is a tendency for the eyelet member to become contaminated with the metal of the electrode. Also, the heat generated may tend to warp or distort the preformed eyelet or tip and thereby change the size of the eyelet passageway.
The Roberson U.S. Pat. No. 3,598,952 discloses a method designed to improve upon the electric resistance welding method by avoiding contamination of the plate by the electrode material and minimizing the amount of electric current needed to effect the weld. In this method, the fabrication is modified to improve the electric resistance welding of the projections to the plate by providing a non-orificed projection to the projection has greater structural strength and is less apt to distort when heated. Also the flange on each projection has a small linear ridge which provides a reduced area contacting the plate. This small ridge offers greater control over the welding operation because the current flow is concentrated in the ridge and because there is greater assurance of complete contact of the flange with the plate. Once the projections are welded to the plate, the holes are drilled through the plate and the projections at the same time to form a continuous passage.
Although the Roberson patented process offers distinct weldng advantages over the Leedy and Russell process, it has its own particular limitations. The drilling of the combined plate and projection must be done with extreme care to assure the hole is concentric with the outside of the projection. Considering that the outside diameter of the projection may be smaller than 0.100 inches and the hole diameter 0.075 inches, there is not much room for error. The process is also limited in that the electric resistance welding of the small ridge to the plate cannot be visually inspected. The weld interface is hidden from view. Also electric resistance welding, because of its character, causes some splattering of the molten metal forming tiny beads that adhere to the plate. Because of the high value of the platinum alloy, care must be taken to recover these tiny beads.
The use of preformed eyelets in feeder fabrication is preferred because it has the advantages of uniformity and easier construction. However, it has peculiar shortcomings as outlined in the Roberson patent. Therefore, if a method for attaching such tiny orificed projections to an orificed plate could be developed which would not distort the size and dimension of the eyelets and its passageway or bore, which could be easily visually inspected, and which could give satisfactory performance during the operating life of the feeder, a substantial contribution would be made to advance the art of glass fiber forming.